The present invention relates to a fluorescent lamp and, more particularly, to a fluorescent lamp which can generate different colour light beams.
A fluorescent lamp of this type can emit, by means of only a single lamp, a plurality of different coloured light beams, and is adapted to construct a colour display device, using the lamp as a display element.
At first, the construction of a conventional color display device will be described.
A first means forms one picutre element of three display elements emitting, for example, red, blue and green, respectively, and performs a colour display by arranging a plurality of those picture elements. It is apparent that the first means includes a number of display elements so that the attachments and maintenance of the display elements are difficult and its display surface cannot be enhanced in density. To eliminate the drawbacks, a second means in FIG. 1 and third means in FIG. 2 have been proposed in Japanese Utility Model Disclosure Sho 61-141763. In FIG. 1, transparent envelope 1 made, for example, of glass has a display end, i.e., light beam transmitting end 1a and electrode sealing end 1b. The inner space of envelope 1 itself is divided by partition member 2 into three parallel discharge paths A, B, C. Each discharge path has anode 3, and is so constructed as to generate a discharge between selected anode 3 and common cathode 4. A fluorescent material layer having different light emitting characteristics at parallel discharge paths is provided on the inner surface of envelope 1 which forms parallel discharge paths A, B, C. Therefore, a number of colours can be displayed by selectively energizing anodes 3. Since partition member 2 divides the inner space itself of envelope 1, the probability of generating colour noises is large. It is further very difficult to provide fluorescent material layers of a plurality of colours on the inner surface of envelope 1 to match the position of partition member 2. In a display element in FIG. 2, three cylindrical partition walls 5 are arranged in the transparent envelope 1. Anodes 3 are provided at the side of beam transmitting end 1a to selectively generate a discharge between a common cathode 4 and a selected anode 3. The inner surfaces of cylindrical partition wall 5 are respectively coated with fluorescent material layers emitting different colours. In FIG. 2, since a fluorescent material layer is not arranged on the inner surface of envelope 1, a difficulty of arranging fluorescent material layers like a display element in FIG. 1 is eliminated. However, since fluorescent material layers formed on the inner surfaces of partition walls 5 are parallel to the center axis, it has such a drawback that the fluorescent material layers cannot be directly observed. Since three cylindrical partition walls 5 are arranged in envelope 1, a dead space exists among three partition walls 5 and the effective light emitting area as observed from the extension of the center axis is reduced. As a result, it has such a drawback that colour noises are increased.